Fluorene based conjugated polymers are known to have interesting optoelectronic properties. Several reports have demonstrated blue light emission from fluorene homopolymers e.g., A. W. Grice; D. D. C. Bradley, M. T. Bernius; M. Inbasekaran, W. Wu, E. P. Woo; Appl. Phys. Lett. 1998, 73, Y. Young and Q. Pei; J. Appl. Phys. 81, 3294 (1997). By incorporating different aromatic functional groups into the polymer chain, fluorene-based conjugated polymers have demonstrated different emissive colors with the emissive spectra spanning the entire visible range (400-700 nm) (M. T. Bernius, M. Inbasekaran, J. O'Brien, W. Wu, Adv. Mater. 2000, 12, 1737). Efficient and stable electroluminescence needs efficient injection of holes and electrons into a light-emitting polymer layer from anode and cathode, respectively. Due to the energy mismatch between the highest occupied molecular orbital (HOMO) of fluorene homopolymers and the work function of the anode (ITO), the hole-injection of fluorene homopolymers is inefficient. U.S. Pat. Nos. 6,309,763, 6,353,083 and 5,879,821 teach the incorporation of triarylamines into fluorene-based polymers as hole-transporting moieties to improve the electroluminescent properties of fluorene-based polymers. US 2004127666 further discovered that the inclusion of tricyclic arylamine in the main chain of a fluorene-based optoelectronic polymer provides further improved conductivity at low voltages as well as higher device efficiency compared to polyfluorenes having other charge transporting groups such as acyclic triarylamines as stated in U.S. Pat. No. 6,353,083.
A need remains for discovering new aromatic amine monomers to develop optoelectronic materials and devices that exhibit improved efficiency and lifetime, and emit light in a variety of colors. Of special interest is a need to discover new aromatic amines that are suitable to be incorporated into fluorene-based polymers to offer deeper blue emission with good hole-injection and hole-transporting properties. It still remains a challenge to design an aromatic amine with wide HOMO-LUMO bandgap (>2.9 eV) to enable a deep blue emission while at the same time to keep the HOMO level to be shallow (close to −5.0 eV) to facilitate hole-injection from anode in a light-emitting device.